1. Field of the Invention
The present invention relates to a toner.
2. Description of the Related Art
In recent years, development in office automation equipment has been experiencing remarkable growth, with the result that image forming apparatuses have been widely prevalent, such as copying machines, printers, and facsimile machines, which use an electrophotographic system.
Electrophotographic image forming apparatuses usually form an image through the following steps: charging electrically a surface of a rotary drive photoreceptor uniformly by use of a charger; exposing the charged photoreceptor surface to laser light emitted from an exposure device so as to form an electrostatic latent image on the photoreceptor surface; developing the electrostatic latent image on the photoreceptor surface by use of a developing device using a toner so as to form a toner image on the photoreceptor surface; transferring the toner image on the photoreceptor surface onto a transfer material (recording medium) by use of a transfer device; fixing the toner image by heating a fixing device so as to fix the toner image onto the transfer material.
In recent years, electrophotography has been advancing in full-color print; in line with that, improvement of toners has been taking place—for example, improvement of binder resins for dispersing a crystalline polyester resin therein so as to improve low-temperature fixability of the toner.
To obtain desirable chargeability, Japanese Unexamined Patent Application Publication No. Hei 1(1989)-284862 suggests carriers in which carrier cores are covered with a silicone resin containing an aminosilane coupling agent.
There were problems to be noticed: A toner was fused with a surface of a developing roller while being stirred in a two-component development apparatus for a prolonged time; a baking phenomenon occurred in which an entire surface of the developing roller was covered with toner components as time passed; and an image density decreased.
It was thought that when the toner components, such as a crystalline polyester and a wax, were exposed on the toner surface, these components—lower in softening point and melting point than an amorphous polyester resin and others—were more likely to fuse with the developing roller surface. It was also thought that the crystalline polyester resin and the monoester-based wax, which were exposed on the toner surface, exuded because of a compression force between the developing roller and a developer, localized friction heat, and rise in temperature inside the two-component development apparatus, resulting in the fusion of the toner components with the developing roller surface. As a result, it was thought that the fused crystalline polyester resin and wax induced the toner to adhere continuously to the developing roller and that the entire developing roller was eventually covered with the toner components.